We propose to examine the hypothesis that the retinal, optic disc and iris neovascularization found in several pathologic ocular conditions occurs in response to a retina-derived angiogenic substance. To investigate this hypothesis we will continue our studies of human intraocular fluid samples. These samples are obtained from patients undergoing therapeutic vitrectomy for various ocular disorders in which retinal, optic disc and/or iris neovascularization is often a complication. The angiogenic activity of these vitreous samples will be studied using existing assays and this activity will be correlated with the clinical status of the eye. Attempts to purify and characterize any angiogenic substances from human vitreal material is impeded, however, by the small quantity of this material available for study. To circumvent this obstacle we will continue the purification and characterization of an angiogenic substance (or substances) which we have recently identified in extracts of bovine, feline, rabbit and human retinas. Information obtained from the study of these more abundant materials will be used to guide the purification and characterization of angiogenic substances from human vitrectomy samples. Eyes containing retinoblastoma, retina-derived tumor, are frequently found to have iris neovascularization. It is possible that a tumor-derive angiogenic substance may be responsible for the phenomenon. Furthermore, this substance may be related to the hypothesized retina-derived angiogenic substance. We will therefore continue ongoing studies of the angiogenic activity of conditioned media from human retinoblastoma cells in culture. The various parameters affecting the liberation and action of human angiogenic substances are not readily amenable to experimental control. We will therefore attempt to develop an animal model in order to better study these parameters. Currently available methods for determining angiogenic activity are somewhat limited in their specificity and sensitivity. We have therefore begun to develop two novel assays of angiogenic activity.